In a typical Virtual Private Network (VPN), a plurality of customer networks, such as LANs, or other user-site based arrangements, interconnect via a core network to provide each subnetwork with the appearance of sharing a common network with each of the other LANs. Each LAN, or subnetwork, has one or more gateway nodes, or customer edge (CE) routers, through which traffic egressing and ingressing to and from the LAN passes. The gateway nodes connect to a network service provider router, or provider edge (PE) router, at the edge of the core network, operable to provide transport to the other subnetworks in the VPN. The CE and PE routers are referred to as “edge” routers due to their proximity on the edge of a customer or provider network. The core network, which may be a public access network such as the Internet, a physically separate intranet, or other interconnection, provides transport to remote PE routers. The remote PE router couples to a remote CE router representing the ingress to a remote subnetwork, or LAN, which is part of the VPN. The remote CE router performs forwarding of the IP traffic to the destination within the remote VPN (LAN) subnetwork.
Conventional VPNs are particularly well suited to the advantages provided by Multi-Protocol Label Switching (MPLS) networks. A major feature of MPLS is its ability to place IP traffic on a particular defined path through the network as specified by the label. Such path specification capability is generally not available with conventional IP traffic. In this manner, MPLS provides separation between the routing and addressing of different VPN customers, and is discussed further in Internet Engineering Task Force (IETF) RFC 2547, concerning Virtual Private Networks (VPNs, or “2547” networks).
Accordingly, MPLS networks are particularly suited to VPNs because of their amenability to forwarding the traffic of multiple customers in a secure manner over service provider networks. Such MPLS networks, therefore, perform routing decisions based on path specific criteria, designating not only a destination but also the intermediate routers (hops), rather then the source/destination specification in IP which leaves routing decisions to various nodes and routing logic at each “hop” through the network.